(a) Field of the Invention
The present invention relates to a test method for a bonding pad on a semiconductor device and, more particularly, to a test method for examining the bonding pads by infrared ray.
(b) Description of the Related Art
A plurality of semiconductor chips formed on a silicon wafer are separated from one another, and subjected to die-bonding onto a package for mounting. Thereafter, the bonding pads on the semiconductor chip are connected to external leads. Current connection techniques in the semiconductor device are classified into two categories including a wire bonding technique and a wireless bonding technique.
In the wire bonding technique, the bonding pads on the chip are sequentially connected to the terminals of the external leads by bonding wires having a diameter as small as 20 to 30 xcexcm. In the wireless bonding technique, all of the bonding pads are connected to terminals on the package by bumps in a single step.
By using the wireless bonding technique, the connection for the bonding pads can be conducted in a single bonding step irrespective of the number of the bonding pads during the mounting process, although the process for the wafer includes complicated steps such as fabrication of bumps. In addition, the semiconductor chip can be packaged in a small size, which is especially suited to a multi-chip module. The wireless bonding technique includes flip-chip bonding, beam-lead bonding, tape carrier bonding, etc.
With the advance of miniaturization technique for LSIs, the thickness of interconnects formed on a chip is generally reduced as well as the thickness of the bonding pads. For example, the thickness of the current bonding pads is as small as 0.6 xcexcm down from the previous thickness of 1 xcexcm. The smaller thickness of the bonding pads is likely to involve damages on the bonding pads or the underlying silicon substrate during the bonding step.
In the wire bonding technique, the damage to the bonding pads can be observed during the bonding step from outside the chip due to the arrangement of the bonding pads, which enables the products having damaged bonding pads to be rejected after the bonding step. However, small amounts of damage formed on the boundary between the bonding pads and the bonding wires cannot be observed from outside the chip. The small damage which is not observed during the bonding step may grow to a larger damage which is, which causes connection faults due to thermal stress during mounting of the resultant package onto a circuit board.
In the wireless bonding technique, such as flip-chip bonding technique, the bonding pads cannot be observed during the bonding step due to the arrangement of the bonding pads being covered by the silicon substrate. As a result, the products having damaged bonding pads cannot be rejected after the bonding step.
It is therefore an object of the present invention to provide a method for testing a bonding pad on a semiconductor chip in a nondestructive process by detecting the damages on the bonding pads which may cause a connection fault in the resultant semiconductor device.
The present invention provides a method for testing a semiconductor chip having a bonding pad on a main surface of the semiconductor chip, the method comprising the steps of irradiating infrared ray onto a bottom surface of the semiconductor chip, receiving the infrared ray reflected from the bonding pad at a photo-sensor, forming an image of the bonding pad from the infrared ray received by the photo-sensor, judging a defect of the semiconductor device from the image of the bonding pad.
In accordance with the method of the present invention, the damages or defect on the bonding pad or on the interface between the bonding pad and the silicon surface or bump can be observed by the image on the monitor, which enables rejection of the semiconductor device having damaged bonding pad or the interface.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.